How to dual boot and not break anything

Dodec · Tux's lil' helper Joined: 09 Jul 2012 Posts: 115

It's been a while, but I'm finally back on the forums because I just got a new computer after my old one died last year. I'm planning on dual-booting it with Gentoo again (it already runs Windows 8, and much as I hate Windows, there are some things I'll still need it for because some people haven't come around to the beauty of open source yet), but my last attempt at that could be described as abortive at best--those of you who recognize me might remember the fact that my very first thread in this forum was something along the lines of "I installed Gentoo, but not all the way, then I took out the LiveCD and it says there's no operating system, what happened to Windows?" "You killed it."

I can't afford to majorly mess up my computer like that again, so to that end, what are some best practices for dual booting that will ensure as much as possible that I don't break everything? I'm on a Toshiba Satellite C55, AMD A6 processor, 4GB RAM, 750GB hard drive, Windows 8.1 v6.3 build 9600. I've already found things like this tutorial, this thread, and this guide, I'd just like to know if there's anything not covered in there that would be good to know to minimize the risk of major issues a la my first time trying to dual boot and having no idea what I'm doing.

Thanks in advance!

Irre · Guru Joined: 09 Nov 2013 Posts: 434 Location: Stockholm

I did it this way (Windows 7)

1) Create a bootable linux usb-stick. Boot linux.

2) Fill free space in all partitions with zeroes: mount /dev/sdaX /mnt ; dd if=/dev/zero of=/mnt/filewithzeroes ; rm /mnt/filewithzeroes; umount /mnt

3) Take a full compressed backup of your harddisk to an external disk: mount /dev/sdbX /mnt; dd if=/dev/sda | gzip > /mnt/sdaimage.gz
(to restore: zcat /mnt/sdaimage.gz | dd of=/dev/sda)

4) Shrink the Windows partition (sda2 in my case)

5) Create new partitions. Install Linux. But do not overwrite existing master boot record mbr (owned by Windows). In stead, install grub and create a new mbr on one of the new partitions. And make that partition active. Configure grub to chainload Windows mbr.

If anything goes wrong. Simply make partion 1 active and windows will boot.

v_andal · Guru Joined: 26 Aug 2008 Posts: 543 Location: Germany

Most likely your new computer uses UEFI, so instead of installing grub into MBR you'll have to install it to UEFI partition. See https://wiki.gentoo.org/wiki/UEFI_Dual_boot_with_Windows_7/8 for some details. If you search for 'gentoo dual boot windows 8' then most likely you'll find more descriptions.

From my own experience, I had to replace (after moving it) EFI/Boot/bootx64.efi on UEFI partition with rEFInd boot loader. All my attempts to configure UEFI with efibootmgr have failed. At first Windows updates would rewrite that file, but in last 2 months this didn't happen anymore. Maybe your UEFI will be more friendly and allow configuration instead of brute force.

I've also had to play with Windows itself in order to squeeze more free space out of its partition. As far as I understand, it puts swap files somewhere around middle of original partition and that prevents aggressive resizes. Disabling swapping would free that space for resize. After resize, swap can be enabled again.

Barracuz · Posted: Fri May 22, 2015 6:12 pm Post subject:

I managed to get gentoo installed and boot windows. I think the key to dual booting (noob here) is the partitioning. As long as you partition correctly you should be fine.

I too followed the same guides you linked. Logged in Windows I defragmented the drives and shrunk the main OS partitiion. Leave it as unallocated space. then booted up the sysrecue cd and used parted to make my partitions. Followed the install as guided in the main handbook Following the ocasional little excerpts for UEFI installs.

I got gentoo going but it's only bootable from the sysrecuecd's grub bootloader. I used both efibootmgr and grub but grub freezes when loading the kernel.

cwr · Veteran Joined: 17 Dec 2005 Posts: 1969

I boot my dual-boot laptop via the windows boot menu, which boots grub in its turn.
It's another five-second delay, but that way, windows doesn't even have to know that
linux exists and all the rebuild partition nonsense is untouched.

Check the use of EasyBCD on the net.

Will

Dodec · Tux's lil' helper Joined: 09 Jul 2012 Posts: 115

So I've been considering all these suggestions and doing some Googling of my own, and it appears that the safest way to go about this is with EasyBCD. Now I just have a couple more minor questions: since I'll be using GRUB2 and not rEFInd, how would that affect the kernel configuration given in https://wiki.gentoo.org/wiki/UEFI_Dual_boot_with_Windows_7/8 ? Will the settings given there be fine, should I just go along with the default suggestions in the Gentoo Handbook, or will I need to change things either way to make the kernel play nicely with both grub and the dual-booting?

DONAHUE · Posted: Sun May 31, 2015 7:51 pm Post subject:

IMHO if you want to UEFI dual boot with windows and not break anything- use rEFInd . The kernel settings given there be fine with grub2. grub2 will be the problem. hints: https://wiki.gentoo.org/wiki/GRUB2#UEFI_with_GPT ; os-prober ; GRUB_PLATFORMS="efi-64" ; make sure you have the ability to rescue windows before grub-install
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The Doctor · Moderator Joined: 27 Jul 2010 Posts: 2678

My trick for not breaking anything is to

0) Back up windows completely. Windows includes tools to do this and it costs 1 DVD to do properly. Very cheap insurance.
1) Do all the shrinking of windows using windows. M$ screws up many things, but handling their own partitions isn't one of them. Linux tools may botch this, so best leave it to windows.
2) Install Gentoo on the newly freed space. Simply adding partitions is simpler than trying to shrink any.
3) For the boot loader, there are a few choices. rEFInd is an option, but it always feels rather clunky to me and windows updates can disable it. On the other hand, simply using efibootmgr is really easy, maintainable, and easily reversible.
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grrilla · n00b Joined: 18 May 2015 Posts: 11

Honestly, so many things can go wrong that if it is really a concern for u, I suggest just buying a big USB stick and creating a VM http://www.techspot.com/guides/809-run-linux-from-usb-drive/

If u do choose to dual boot just stay calm through the process, often we have a habit of thinking "It's F*cked!!". When actually it's completely recoverable with a rescue boot and some config file changes (grub, fstab etc)

Dodec · Tux's lil' helper Joined: 09 Jul 2012 Posts: 115

So...I shrank the Windows partition and all that, and now I'm noticing something weird as I'm trying to draw up my Linux partition plan. Since it was really more of a partitioning question rather than a methodology question, though, and I don't want to derail my own thread, I posted it in the partitioning sticky.